The standard lexicon for reporting adverse events in National Cancer Institute (NCI) sponsored clinical trials is the Common Terminology Criteria for Adverse Events (CTCAE), which consists of 790 individual items. Historically, adverse events have been reported by clinicians. However, multiple studies have found that clinicians tend to underreport symptom severity and onset compared with patient self-reports. In 2008, the NCI contracted a multi-institution consortium to develop a patient-reported outcome (PRO) counterpart instrument to complement to the CTCAE. This system, called PRO-CTCAE provides a web-based platform to collect patient reports of symptoms they are experiencing during treatment for the purpose of enhancing adverse event (AE) reporting. The overall goal of the PRO-CTCAE initiative is to employ rigorous scientific methods to create a system for patient self-reporting of adverse symptoms in cancer trials that is widely accepted, generates useful data for investigators, regulators, clinicians and patients; and is compatible with existing systems for reporting adverse events. 81 symptoms were identified in the CTCAE to be amenable to patient reporting; the measured attributes for each symptom include frequency, severity, and activity interference. Questions and response options were standardized, along with plain language terms for each symptom. A web-based platform was developed and tested for administering the PRO-CTCAE items. The prototype has undergone undergoing testing to assess usability, logistical feasibility, and validity in a variety of cancer care settings. The PRO-CTCAE system has the potential to enhance adverse event reporting by integrating patient experiences and can foster consistency of data collection methods across studies.